Generally, light emitting devices such as neon lamps, CCLs (cold cathode lamps), LEDs (light emitting diodes), etc. are widely used in outdoor electronic display boards. EEFLs (external electrode fluorescent lamps), CCFLs (cold cathode fluorescent lamps), LED electronic displays, etc. are used as indoor light emitting devices.
Neon lamps or CCLs use high voltage power and thus have disadvantages of high power consumption, risks of electric shock or fire, and a short lifetime. On the other hand, EEFLs or CCFLs have problems in being used outdoor because they use high frequency. Furthermore, EEFLs or CCFLs have disadvantages of low intensity of illumination and a short lifetime.
Electronic display boards using LEDs are characterized in that light is emitted in one direction because a rear surface of the board that is opposed to a light emitting surface is covered with a cover for arrangement of wires or black background treatment.
Recently, light emitting devices are used not only as lighting but also as advertising signboards or interior decorations for beauty.
However, the above-mentioned light emitting devices are limited in enhancing aesthetic effects because of the size of a lamp or the size of a stand for supporting a light emitting device.
To enhance aesthetic effects, transparent electronic display boards were introduced, in which a plurality of light emitting elements provided on transparent electrodes emits light and thus displays text or a figure on the transparent electrode and plays a video under the control of a controller. In such a transparent electronic display board, a plurality of light emitting elements is wired on transparent electrodes. Typically, light emitting elements each having two, three or four electrodes are used. Of conventional transparent electronic display boards, a wiring diagram of a transparent electronic display board having four-electrode light emitting elements is illustrated in FIG. 1.
FIG. 1 is a perspective view showing a conventional transparent electronic display board. FIG. 2 is a sectional view of FIG. 1.
Referring to FIGS. 1 and 2, the conventional transparent electronic display board 1 includes: a pair of transparent plates 11 and 12 that are spaced apart from each other and adhered to each other by a transparent resin 40; a transparent electrode 30 that is formed by applying conductive material on surfaces of the transparent plates 11 and 12 that face each other and is able to transmit electric signals; light-emitting elements 20 that are adhered to the transparent electrode 30 by a conductive adhesive and non-conductive adhesive; and a transparent resin 40 that is injected into space between the transparent plates 11 and 12 including the light-emitting elements 20 so as to adhere the transparent plates 11 and 12 to each other and fix the light-emitting elements 20 in place.
The transparent plates 11 and 12 include: a first transparent plate 11 to one surface of which the transparent electrode 30 and the light-emitting elements 20 are fixed; and a second transparent plate 12 adhered to an upper surface of the first transparent plate 11.
The transparent electrode 30 is formed by applying any one of ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), and liquid polymer, which are conductive materials, to a surface of either transparent plate 11 or 12 that faces the other transparent plate 11 or 12.
After applied to the entirety of the surface of the first transparent plate 11, the transparent electrode 30 is partitioned into a plurality of parts to be connected to anode electrodes and cathode electrodes of the light-emitting elements.
Each light-emitting element 20 includes one or more anode electrodes and a cathode electrode. Furthermore, the light-emitting element 20 further includes: terminals 30 that are made of conductive metal and are provided to transmit an electric signal between the anode electrodes and the transparent electrode 30; a light-emitting chip 21 connected to and placed on the terminals 23; a lens 22 that is provided on an upper surface of the light-emitting chip 21 so as to diffuse light; a conductive adhesive 24 adhering the terminal 23 to the transparent electrode 30; and a non-conductive adhesive 25 that insulates partitioned parts of the transparent electrode 30 from each other and adheres the light-emitting element 20 to the transparent plate. The light-emitting element is a well known technique; therefore, further explanation of the construction and operation thereof will be omitted, but the structure of fastening light-emitting element to the transparent plate will be described in brief.
In the conventional transparent electronic display board, the transparent resin 40 is charged into space between the first transparent plate 11 and the second transparent plate 12 and then hardened to fix the light-emitting elements 20 on the surface of the first transparent plate 11 and protect the light-emitting elements 20.
The light-emitting element 20 comprises a front light-emitting element that emits light when an electric signal is applied thereto through the transparent electrode 30. Light emitted from the light-emitting element 20 is output to the outside through the transparent resin 40 and the second transparent plate 12.
The conventional transparent electronic display boards having the above-mentioned construction are installed on buildings, parks or indoor space to display numerals, letters or figures for advertisement or are widely used as decorations. Recently, transparent electronic display boards that can play videos were introduced, whereby the usefulness thereof is further increasing.
Here, to play a video using the transparent electronic display board, the number of light-emitting elements must be increased compared to that of the typical transparent electronic display board for displaying letters or figures, because the quality of displayed video images can be improved when the distance between the light-emitting elements is reduced. However, in the conventional transparent electronic display board, areas on which the transparent electrodes are wired must be considered in installation of the light-emitting elements on the surface of the first transparent plate 110. Thus, the number of light-emitting elements is limited. As such, the conventional transparent electronic display board is problematic in that there is a limit in reducing the distance between the light-emitting elements because the arrangement of the transparent electrodes and the areas for installation of the light-emitting elements are taken into account.